US1901706A - Production of pulp - Google Patents

Description

March 14, 1933- T. L. DUNBAR 1,901,706

PRODUCTION OF PULP Filed April 16 1952 MIME/VTOR Patented Mar. 14, 1933 UNITED STATES PATENT om moms LEONIDAS nurses, or wArnR'rowN, NEW YORK, ASSIGNOR TO CHEMIPULP PROCESS, INCORPORATED, or warnnrown, NEW YORK, A CORPORATION on NEW YORK rnonuorroiv or PULP Application filed April 16, 1932. Serial No. 605,696. 1

This invention relates to the production of pulp, andv in particular to the production of a super-quality sulphite pulp for use in the manufacture of paper.

It is an object of my invention to provide a process capable of producing a sulphite pulp from which may be made sulphite paper of unusually, high strength' A further object is to provide a process for the production of sulphite pulp capable of giving a higher yield of pulp than is obtainable by processes now in use.

7 Further, it is my object to produce a highcellulose pulp from which may be made a. paper similar to kraft in strength, but more pliable than kraft. a A further object is the provision of a flexible process capable of variation of produc- 1 ing pulp with varying characteristics as may be desired.

. A still further object is the provision of a sulphite process by the use-of which a savmg of acid is effected.

The higher strength of kraft pulp is due primarily to residual lignin, which is-not removed by the kraft process. While my improved process removes'the greater part of this residual lignin and pentosans, in

doing so it leaves a-cellulose of unusually high strength, thereby imparting highly desirable characteristics to the finished product.

Briefly, in the practice of my improved process the digester is first filled with raw material and bisulphite liquor in accordance with the disclosure of my United States Patents Nos. 1,646,084 and 1,699,234 and- Dunbar et al U. S. Patent No. 1,699,056. A working pressure and temperature sufficient to release extractives from the raw material is then built up and the digester is closed in for a soaking. period suitable to the wood conditions as hereinafter pointed out. The bisulphite liquor is then drained from the digester and may be conducted to a the acid settling tank or to other parts of.

prepared the .acid system where partially .liquor is contacted with ]iquors om the digester. The raw materialis then subjected to a bisulphite cook in accordance lime acid EEl'SSUED tower. This isshown by way of example a only, as the applicability of my invention is not limited to the milk of. lime system, but is equally applicable to thelimestone tower system. 2 is a line leading from the tower 1 to the settling tank 3. From the settling tank, the line4 leads to the pump 5, which forces the liquor into the acid storage tank 7 through the line 6. Th'epump 8 forces the liquor from the storage tank 7 through the line. 9 to the eductor 10, where it is contacted with relief fluids from. the digesters 15. Although four digesters are shown, any number may be used.

The drop or condenser leg 30 leads from the eductor 10 through the exchange heater 23 -to the bottom of the accumulator 11.

12 is a pump for forcing the bisulphite liq- 16 is a valved branch leading from the 7 top of each digester for venting relief gases and fluids through the header 17 to the eductor 10, while 22 is a valved side relief branch .for conducting liquors from the digester to J V the header 17. The valved branch line 25 i leads from the top of the digester to the header 27, which header discharges into the acid storage tank 7. 26 is a valved branch off from the-line 25, venting to the atmosphere. The operation of these vent lines has been fully described in my copending application Ser. No. 446,046, now Patent 1,859,384 dated May 24, 1932. Liquor may be drained from the digesters through the strainer.18,-the line 20 having therein the valve 19, and the header 21 leading back to the settling tank 3.

In .the practice of my improved process, .[I may proceedas follows:

The digester having been charged with chips, the valve in the branch 26 is opened and the digester is filled with hot bisulphite liquor from the accumulator 11 by means of the pump 12,- line 13 and valved branch 14, in accordance with the disclosure of my co-pending application, Ser. No. 446,046. When the digester has been filled, the valve in the branch 26 is closed and a pressure of approximately 50 pounds is applied to the contents of the digester by running the pump 12 until this has been accomplished. The valve in the line 14 is then closed and the pump 12 shut down, and the chips are subjected to a soaking or penetration period under pressure, with all the valves of the digester lines closed.

The duration of this soaking period, as well as the temperature, will vary with the kind and quality of the raw material, and with its initial moisture content, this soaking period being preferably continued until the extractives (by which I mean the so called Water-solubles) are released from the material and all the raw material is placed in a constant state as regards moisture content. The bisulphite liquor penetrates the chips to some extent, leaving a deposit of acid salts. These soften the encrusting material and the subsequent digestion thereof is expedited. In addition, this initial penetration may partially insulate against too drastic a digestive action in the succeeding stage of'the process.

At the termination of this soaking period, the bisulphite liquor is drained out of the digester through the valved line 20 and is returned through the header 21 to the acid settling tank, where it is mixed with partially prepared liquor from the acid system. The liquor is then pumped from the settling tank to the acid storage tank for reuse. Normally, the acid system is operated continuously and therefore the contents of the settling tank are being continuously pumped to the acid storage tank. The extractives contained in the bisulphite liquor drained the extractives, resinous matter and lignin back to the settling tank are neutralized by an excess of alkaline base in the raw liquor. After the soaking period has been completed and the liquor has been drained from the digester, the digester is again filled with hot bisulphite liquor, steam is admitted to the digestert-hrough a line (not shown) and the cooking is carried on in the usual manner until a large part of the lignin content of the wood is removed. This stage of'my improved process differs, however, from the acid cook as practiced in the present singlestage process. In the single-stage process,

are substantially dissolved out by acid. This produces, particularly toward the end of the cook, chemical compounds which have a deteriorating effect on the fibres. In my im- 1,9o1,7oo 1 proved process the formation of these com-. pounds is to a large extent prevented, due to the fact that upon their appearance in quantities which would injure the cellulose, the cook is stopped, all or a part of the bisulphite liquor is drained from the digester,

and the material is then treated in a third stage with precipitated lime (or other suitable alkaline) water.

The length of time required to. carry out the second. stage of my process is a function of the strength of the liquor and of the temperature employed. \Vhere it is necessary to make short cooks, the maximum temperature employed will be approximately 10 C. higher than will be the case if more time is allowable. If the bisulphite liquor runs relatively high in free S0 the time required as well as the temperature can be reduced, although when operating with abnormally high free acid content difiiculty may be experienced in recovering the acid economically. I have obtained excellent results by operating with a bisulphite liquor of approximately (3% free S0 and approximately 1.25% combined.

I have found that it is sometimes desirable, in order to produce special grades of pulp, to repeat the cook, or second stage of my process. In this case, a part only of this cook is accomplished with each separate charge of bisulphite liquor and consequently there is a progressive increase in the maximum temperature for each recooking. For example, I have found that in the production of a sulphite pulp with the strength characteristics of a high grade kraft pulp, the cook itself may be carried out in three stages, the maximum temperature during the first being 110 (1., during the second approximately 120 C. and during the third approximately 132 C.

After the completion of the cook, the valve 19 is again opened and all or part of the digester liquor is drained back to the settling tank for'reuse, the solutes therein being neutralized by the addition of an alkaline liquor. The digester is then filled up (as, for example, by means of the connection 32) with precipitated lime water, and the contents of the digester are boiled or cooked under the heat still remaining in the pulp until the desired pulp is obtained. It is sometimes necessary to add more heat during the lime water cook, and this may be accomplished in the usual manner by admisslon of steam into the digester, or if the digester is provided with indirect heating coilsthe contents of the digester may be indirectly heated by the admission of steam to these coils.

After this last cooking with precipitated lime water, the pulp may be blown into a blow pit or other suitable draining medium in the usual manner, viz., normally the blowoff valve (not shown) at the bottom of the digester is opened and the contents of the digester are forced out by the pressure existing therein. In some cases it is possible to carry out the alkaline cook in the blow pit or elsewhere, after the stock has left the digester. The liquor that drains -ofl from the blow pit is conducted to settling or clarifying tanks for reuse.

The precipitated lime water has a mildly alkaline reaction and neutralizes any ligno sulphonic acids which may remain in contact with the cellulose fibres after the acid cook. This action produces a much stronger and more. pliable pulp than that produced by the single stage acid cook process and gives the pulpmany characteristics ofkraft pulp which is produced by the alkaline process. Q

The strength and folding characteristics of the pulp may be varied by varying the point in the digestion process at which the precipitated lime (or other alkaline) water is applied. For example, if a pulp is desired having strength characteristics nearly the same as ordinary sulphite pulp, the second stage, or bisulphite cook, of my process ismagnesium in addition to the calcium pres-' ent.

The applicability of my process is not limited to the spruce, hemlock and fir ordinarily used for the production of sulphite pulp. By my process I am able to produce a novel sulphite. pulp having an unusually high mullen, tear and fold test, but much more pliable than kraft pulp.

I claim 1. A process for-the production of pulp which comprises soaking fibrous material in heated bisulphite liquor under a pressure of approximately 50 pounds until the extractives are substantially removed therefrom and the liquor has penetrated the chips, draining the bisulphite liquor from the fibrous material and mingling said liquor with fresh liquor for reuse, digesting the fibrous material under heat and pressure in bisulphite liquor until the lignin is substantially removed therefrom, withdrawing bisulphite liquor from the material and mingling it with fresh liquor for reuse, and cooking the fibrous material in alkaline liquor until the incrustants of the cellulose are substantially removed.

2. A process for the production of pulp which comprises soaking fibrous material in heated bisulphite liquor under'pressure until the extractires are substantially removed 1 I therefrom and the materlal is of uniform moisture content, withdrawing the bisulphite moved therefrom and the liquor has penetrated the chips, draining off the bisulphite liquor and mingling it with fresh liquor for reuse, digesting the fibrous material in bi-' sulphite liquor under, heat and pressure to remove lignin therefrom, draining off liquor from'- the material, and finally cooking the material in precipitated lime water.

4. A process forthe production of sulphite pulp which comprises soaking fibrous material in bisulphite liquor, draining off the liquor, digesting said material under heat and pressure in additional bisulphite liquor, and finally cooking said material in alkaline liquor.

5. process for the production of sulphite pulp which comprises first soaking wood chips in bisulphite liquor under pressure, then cooking the chips in bisulphite liquor under pressure at a temperature above 100 C., and finally cooking in precipitated lime water.

6. In the production of sulphite pulp, charging a digester with fibrous material, filling the charged digester with bisulphite liquorfrom an accumulator and soaking the fibrous material in the digester under heat and pressure until the extractives are substantially put into solution, withdrawing liquor from the digester and returning it to the accumulator, refilling the digester with bisulphite liquor from the accumulator and digesting the fibrous material in the digester under heat and pressure to' remove lignin therefrom, withdrawing liquor from the i: gester, adding alkaline liquor to" the diadmitting precipitated lime Water thereto and cooking the material therein.

8. In a process for the production of pulp, soaking fibrous material in bisulphite liquor 5 under heat and pressure until the extractives are substantially removed therefrom and the liquor has penetrated the chips, draining liquor from the fibrous material, then subjecting the fibrous material to a series of digestion processes in bisulphite liquor under heat and pressure, andfinally cooking the fibrous material in alkaline liquor.

9. In a process for the production of pulp, soaking fibrous material in bisulphite llquor under heat and pressure until the extractives are substantially removed therefrom, then subjecting the fibrous material to a series of digestion processes under pressure and at successively higher temperatures, and finally cooking the fibrous material in alkaline liquor.

10; In a process for the production of pulp, charging a digester with fibrous mate-- rial and soaking said material therein in bisulphite liquor under heat and pressure to i remove extractives therefrom, Withdrawing liquor from the digester, refilling the digester with bisulphite liquor and digesting the fibrous material therein under heat and pressure to remove lignin therefrom, discharging the fibrous material from the digest'er and thereafter cooking the fibrous material in alkalineliquor. 4

11. A process for the production of sulphite pulp which comprises first soaking fibrous material in bisulphite liquor under heat and pressure until extractives are substantially removed therefrom and the material is of uniform moisture content, then 40 digesting the fibrous material in bisulphite liquor under heat and pressure until the formation of ligno sulphonic acid reaches a point deleterious to the material, and finally cooking the fibrous material in alkaline liquor-until the incrustants of the cellulose are substantially removed therefrom.

12. Sulphite pulp obtained by soaking fibrous material in heated bisulphite liquor under pressure until the extractives are substantially put into solution and the bisulphite has penetrated the fibrous material, Withdrawing said liquor, cooking the material in fresh bisulphite liquor under heat and pressure, Withdrawing said liquor, and

cooking the material in alkaline liquor.

" THOMAS LEONIDAS DUNBAR.

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